DR3 (TRAMP, LARD, WSL-1, TNFRSF25) is a tumor necrosis receptor family member expressed specifically on T cells that is most similar to TNFR1. The ligand for DR3 is TL1A, a TNF family member protein reported to be expressed by endothelial cells. TL1A can costimulate T cell activation in vitro, but the physiological sources of TL1A and its in vivo role in peripheral T cell biology are not known.
Interactions between numerous TNF family ligands and receptors play an important role in shaping specific features of T cell responses. A subfamily of TNF receptors including CD30, TNFR2, OX40, CD27, GITR, HVEM, and 4-1BB are expressed on T cells and mediate distinct aspects of costimulation in specific T cell subsets (Croft, 2003). For example, OX40 potentiates post-activation survival of activated CD4+ T cells (Croft), TNFR2 costimulates CD8+ T cell activation, and GITR has a unique role in regulatory T cells. DR3 (TNFRSF25/TRAMP/LARD/WSL-1) is a death domaincontaining TNF-family receptor that, like its closest homolog TNFR1, recruits TRADD and has the ability to activate NF-kB and MAP-Kinases or, alternatively, trigger caspase activation and programmed cell death on the cellular context. Unlike TNFR1, DR3 is specifically expressed in lymphocytes with the highest levels on T cells. However, the function of this receptor in T cell homeostasis is not well understood, particularly since the authentic ligand for this receptor, TL1A, was only recently identified. Initial reports suggested that TL1A was expressed exclusively on endothelial cells, and addition of exogenous TL1A was reported to costimulate IL-2 and IFN-γ production by human T cells stimulated though the TCR (Papadakis et al., 2004; Papadakis et al., 2005). More recently, TL1A has also been found at sites of inflammation such as in inflammatory bowel disease (Bamias et al., 2003; Bamias et al., 2006).